Jamal needs 8 hours to do a job. Kamal takes 10 hours to do the same job. How long should it take Kamal & Jamal working together to do the job?

A 5 hours

B 41/2 hours

C 21/2 hours

D 44/9 hours

Correct Answer: Option D

In 8 hours, Jamal does 1 job

In 1 hour, Jamal does 1/8 job

Again,

In 10 hours, Kamal does 1 job

In 1 hour, Kamal does 1/10 job.

Now,

In 1 hour, together they will do (1/8 + 1/10) job

= 18 / 80 job

= 9/40 job

Thus Together,

They do 9/40 job in 1 hour

They do 1 job in 40/9 hours

&nb